Max langer



M. LANGEFI.

TELEPHONE SYSTEM.

APPLICATION FILED JUNE 23, I9I4. RENEWED APR. 10,1919.

1,322,247. Patented Noms, 1919.

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M. LANGER.

TELEPHONE SYSTEM.

APPLICATION HLD1uNE23.|914. RENEWED APR. 10,1919.

Patented Nov. 18, 1919.

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M. LANGER.

TELEPHONE SYSTEM.

APPLICATION FILED IuNE 23, I9I4. RENEwED APR. 10.1919.

1,322,247, l Patented Nov. 18, 1919.

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MAX LANGER, OF CHARLOTTENBURG, NEAR BERLIN, GERMANY, ASSIG-NOR T0 SIEMENS & HALSKE, A.G., 0F SIEMENSSTADT, NEAR BERLIN, GERMANY, A CORPORATION 0F GERMANY.

TELEPHONE SYSTEM.

Specification of Letters Patent.

Patented Nov. 18, 1919.

Application filed June 23, 1914, Serial No. 846,813. Renewed April 10, 1919. Serial No. 289,134.

To all whom it may concern.'

Be it known that I, MAX LANGEE, a citizen of the German Empire, and residing at Charlottenburg, near Berlin, Germany, have invented certain new and useful Improvements in Telephone Systems, of which the following is a specification.

My invention relates to telephone systems in which connections are established over selectors and testing takes place over the talking wires.

The connections for the switches and the trunk lines between the switches in telephone systems worked automatically or semi-automatically are generally made by means of three branches. The branches generally known as the a-'branch and the ZJ- branch are used for adjusting the switches and for the talking service, while the third bra ch known as the c-branch or the private line is used for testing, engaging, releasing and like operations. In order to save the expense of the third branch for trunk lines between offices located a long distance apart, translators may be connected into circuit at the outgoing end ofthe trunk line, say in the manner described in the German Patent 205268. The switches are then arranged for three branches, butl the trunk line has two branches. F or simplifying the switches it has also been proposed to test over the talking branches. In this case the talking line runs over the testing contact of the switch, as described, for example, in the United States Patent 709739 to Albert M. Bullard, dated Sept. 23, 1902. In consequence of the resistances being exactly balanced the testing contact is exactly at the potential of the testing battery during the conversation. As n0 current flows through the testing relay the conversation is not disturbed by troublesome clicking noises.

This arrangement is dependent, however, on the exact equalization of the resistances and cannot be employed when a switch, c. g. a selector, is to be used sometimes for a con-v nection in its own otlice and at other times for a connection to a remote office, for in this case the very different resistances of the trunk lines come into play.

A primary object of my invention is to enable the switches and the trunk lines to be made for two branches, and to enable testing to take place over the talking branches without regard being paid to the various resistances at different times, e. g. as when connections are made in the home or to a remote office.

To this end, I arrange that on those sections of the two talking wires, over which testing is to take place, falls of potential of equal magnitude are produced in the same direction during the conversation. Then, when testing on a busy line through the testing relay, which is bridged between two symmetrically located points of the talking wires, no current flows and no disturbance of the conversation is caused.

Connections are known, in which the lines between the switches are disconnected from the battery during the conversation. In this case also, when a testing coil is connected over such a line no current can arise.

The falls of potential on the two talking wires are unequal during the adjustment of the switches and also, under certain circumstances, during metering, releasing and like operations. Another object of my invention is to provide that regular testing may take place on lines over which any service operations affecting the switches are taking place at the moment of testing. It is true that currents will then flow through the testing coil, but I select the resistance conditions on the talking wires such that the service operations remain undisturbed and that the current liowing through the testing relay does not suiiice for energizing it.

Arrangements are also known, in which duringk the adjustment for lifting the selectors, for example, only the a-branch is used, while the ZJ-branch is currentless, and in which for revolving the selectors only the o-branch conducts current while the a;- branch is currentless. In this case no current is present in the testing relay as the one talking branch is isolated or 1s weakened by high resistances.

To these and other ends described hereinafter, my invention consists in the construction, arrangement and combination of parts described hereinafter and pointed out in the claims.

@ne illustrative embodiment of my invention and a modification thereof are diagrammatically represented by way of example in the accompanying drawings, wherein Figures l, 2 and 3 show a telephone system inwhich the current impulses are sent through ground connections of the talking wires to the subscribers station over the one a-branch, while a current flows permanently over the other branch Similar reference characters designate like parts in all the figures.

Referring to Figs. l, 2 and 3 the system shown operates as follows Vhen the receiver is removed from the switch hook at the station N1 the following circuit is closed: ground, battery, left hand winding of relay R, back contact t3, line conductor a, station N1, line conductor Z), back contact 252, right hand winding of relay R, ground. When the wipers of the line switch VW are advanced until the private wiper cv engages an idle trunk line, a circuit is completed from ground through battery, working contact 71 in parallel through the relays T and z, wiper co, conductor c, resistance w1, in parallel through resistance Q02, back contact mi, to ground, and through relay C, primary 7off normal contact is, to ground. In this circuit the relays T and C are energized and, therefore, the working contacts t6, t, closed. Consequently the following` circuit is completed; ground, battery, relay A, left hand winding of the differentially wound relay X, trunk line (L, working contact t2, station N1, working contact t trunk line b, right hand winding of relay X, relay B, ground.

The calling subscriber now operates his calling dial in the usual manner thereby grounding the relay B at the station N2. When the relay B is momentarily denergized the dierentially wound relay X is energized. As the calling dial returns to its normal position, the relay D is again en ergized by the following circuit: ground, battery, Working contact w1, relay B, ground. By closing the make contact m2 the relay X also prepares the circuit over ground, battery, lifting magnet H, contact a02, contact a of relay A, shaft contact 10701 and ground for the lifting magnet H. The current impulses sent over the t-branch on the return of the dial are transmitted by the relay A, in conse-- quence of its opening and closing its break contact al, to the lifting magnet H of the first selector I GV.

On the return of the dial into its normal position the ground at the station is removed and the relay X releases its armature, while the relay B remains energized. During the lifting impulse, the contact 7:, in the circuit of the relay C opened at the first step of the shaft. The relay C remains grounded, however, over its own contact 0 the contact 603 and the contact m2. On the relay X being denergized at the termination of the first series of impulses the relay C also releases its armature owing to the contact m3 being opened. The rotary magnet D is now energized over ground, battery, interrupter U, relay D, contact l, contact c2 and ground and rotates the switch arm of the first selector I GWV until the relay C is energized again. This occurs on the switch arms J1 and J 2 arriving on a trunk line VL leading to a free second selector H GV, a second coil 2 of the relay C being bridged by the closed make contact b2 of the constantlyv energized relay B over the two talking wires leading to the next selector. The coil 2 of the relay C thus serves as a test relay.l lVhen the switch arms J1, J2 arrive on a free trunk line VL a circuit for the relay A2 and the test coil 2 of the relay C is closed over the following circuit, viz: ground, battery (in the second selector H GV), relay A2, end contact 7a2, contact p1, switch arm J1, contact b2, relay C, contact c3, switch arm J 2 contacts p2, 7c3, a2 and ground. On the relay C being energized the circuit of the rotary magnet is broken at the contact 02, so that the first selector stops. The relay C simultaneously closes its contacts c1, c4 and 05. The talking wires are connected by the contacts c4 and c5 to the second selector H GV and the test coil 2 is disconnected at the contact 03. The rela-y C now remains energized in the circuit over ground, battery, c-branch of the preselector VlV, resistance w1, coil l of relay C, contact 0 the shaft contact @0702 closed at the rst rotary step of the selector, contact m2 and ground until release takes place.

On the relay A2 in the test circuit being energized the contact a2 is reversed from ground to the Contact co2, and the b-branch of the connection over the relay B2 is thereby connected to the battery. The excitation of the relay B2 causes the junction line to be busy. The test coil C of any selector which now tests cannot receive any current because the two branches aand b are connected over the relays A2 and B2 to the same pole of the battery. lVhen the subscriberV rotates his dial a second time the relays A and X are energized, whereby both the branches fr. and b in the first selector I GFW are grounded. The relay A closes the contact a2 and the relay X closes the contact m2. On the return of the dial of the dial switch N, the subscribers branch a becomes currentless and the relay A is denergized. The contact e., opens as frequently as the branch a is broken in the dial switch N1, and the relay A2 releases its armature just as often. The circuit over the b-branch for the relay B2 remains established over ground, battery, relay B2, contacts b3, p2, switch arm J 2, contacts c5, resistance 'L02 or contacts at, 00,2, ground, however, and the contact b2 in the circuit ground, battery, lifting magnet H2, contacts b4, a5, and ground for the lifting magnet H2 of the second selector Il GW remains closed. The impulses are transmitted by the make contact a, of the relay A2 to the lifting magnet. During the interruptions in' the a-'branch for the current impulses and during each denergization of the relay A2 it is true that the contact a2 is also closed. This, however, exercises no further action on the switching operation. 'On the'return of the dial into its normal position the denergized relay X disconnects the ground from the b-branch of the trunk line at contact m2, so that the relay B2 is denergized. Vhile the b-branch is currentless the relay A2Y remains energized over ground, battery, relay A2, resistance w22, contact p1, switch arm J1, contacts c2, a2, resistances 105, w, contact s2 and ground, and holds its make contact au closed. The following circuit for the rotary magnet D2 is thereby established, viz: ground, battery, interrupterU2, relay D2, contacts as, p3, b5, and the contact 70,2 closed at the lirst lifting step of the shaft, and ground, and the switch arms J 2 and J 2 of the second selector H GlV are rotated. This circuit remains established until the contact p3 opens. The contact b2 in the same circuit remains closed because the relay B2 does not attractrits armature again before the relay P2 is energized. The make contact c, in the b-branch in the first selector is closed, before the relay B2 is energized, 'by means of a relay V which is energized in the circuit:-ground, battery, relay V, contact x5, ground, this relay V being energized during the energization of the relay X over its make contact 005, and ground is thereby connected over resistance wl and contact s2 to the ZJ-branch of the trunk line. The relay B2 is disconnected, however, from the ZJ-branch both at contact b2 and also at the oft' normal contact 7c3, because this contact 702 opened at the first lifting step of the shaft.

The test circuit o'f the second selector II GWV is as follows contact arm J 3 contacts a2, b2, relay P2, switch arm J 2. The selector advances until it finds a free third selector. The disengagement of a third selector is indicated exactly like the disengagement of a second selector by a make Contact al, of the relay 'A3 being grounded and the (JL-branch of the trunk line being connected over the relavA2 of the third selector to the battery. When free third selector is found the following circuit is established, viz: ground, battery in the third selector III GV, relay A2, the a-branch of the trunk line, switch arm J 2, make contact a, of the energized relay A2, break contact I), of the denergized relay B22, relay P2, switch arm J 2, Zrbranch of the trunk line, contact cl2, ground in the third selector Hl GV. The relay P2 in this circuit is energized and the circuit for rotating the rotary magnet D2 is thereby opened at contact p2. The second selector II GV remains stationary. The engaged line to the third selector is busy as before,

and the second selector II GWV is busy owing to the relay A3 attracting its armature and switching over the Zi-branch of the trunk line from ground to battery, so that the two branches of the trunk line are connected to the same pole. When the relay P2 in the second selector is energized it reverses the contacts p2 and 792 and closes the contacts p2, p5 and p6. The following bridge is thereby placed over the talking wires in the second selector, viz: a-branch of the trunk line, con tacts p5, p2, P1, relay A2, relay B2, contact p2, relay P2, b-branch of the trunk line. The talking line is connected through at the contacts 102 and 292. The resistance of this talking bridge is several thousand ohms, so that no appreciable loss of talking current is caused. The bridge is connected in order to be able to exercise an influence on the releasing magnet of the second selector over the talking wires. This influence must take effect over the talking wires because no auX- iliary branches exist. Release is effected on the relays A2 and B2 being simultaneously denergized. Consequently, in the following periods of series of impulses at least one of the two relays A2 and B2 must remainrenergized. The bridge to be connected over the contacts a7, Z), and the relay P2 is not made during the subsequent series of impulses because the condition of the two relays A2 and B2 subsequently no longer admits of the contacts a7 and 56 being closed simultaneously.

The object of the resistances ws to L07 is to cause the busy trunk line between the first and second selectors to appear busy during the emission of impulses. The testing of the first selector with the coil C is based on both branches of busy lines being connected to the like pole of the battery, whereas in the case of the free lines in the following selector the one branch is connected to the battery and the other to ground. During the emission o'f impulses, however, as mentioned above the. lli-branch is connected to ground, i. e. over the contact 032 in the first selector, while the a-branch is periodically connected to the battery when the impulse contact a2 is open, but is connected to ground over the contact .r2 when the contact a2 is closed. As long as the contact a2 is open during a series of impulses a testing selector could connect its test coil C in parallel with the contact arms J 2 and J2 and the following circuit would be established for the testing selector, viz: ground, battery of the enlthe testing selector, the coil C of the testing selector, the switch arm J2 of the testing selector, the multiple connection at the banks of contacts of the selector, the switch arm J 2 of the selector I GWV shown in the drawing, contact :v2 in the illustrated selector, and ground. This would cause a double connection. To prevent this, at the moment the contact c, opens the contact d2 also opens. The resistance w, is now so great that the relay B2 at the illustrated selector still just holds its armature becauser it was previously energized, but that a test relay C in the above-described test circuit does not receive sufficient current over the resistance w3 'for attracting its armature.

At the moment of the change from lifting to rotation of the second selector, z'. c. at the moment when the contact ai, has opened after the emission of impluses, but when the relay V still holds the contact c, open, the two branches of the talking line are likewise unsymmetrical. Thus a test coil C of a testing selector connected in parallel with the switch arms J, and J2 of the illustrated selectors could obtain current in the following circuit, viz: ground, contact s, in the first selector I GlV, resistance co6, contact o2, c-branch of the trunk line, contacts ai, c2, switch arm J1, multiple connection, contact arm of the testing selector, coil C, second contact arm of the testing selector, multiple connection, o-branch of the trunk line, contact p2 in the illustrated second selector H GW, contacts 7c3, t3/relay B2, battery and ground. In order to keep this current very small the retardation relay V in the first s'elector opens the contact c2 and connects the resistance to, into this circuit. This resistance to, is so large that the current flowing through the test coil of a testing selector is too small to energize the testing relay C. The holding` circuit for the excitation of the relay A2 over the contact s, in the second selector is, however, maintained in spite of the resistance rbeing cut in.

Also, during the rotation of the second selector there would be want of symmetry on the two branches of the line. The b-branch is currentless because the relay B2 is entirely disconnected from it. The contact c, will have closed some little time after the second selector has started to more. The condition is then as follows: a current liows on the ii-branch from ground in the first selector I GW, over contact 8 resistance 10G, ovel1 the now closed contact o2, a-branch of the talking line, Contact p, in the second selector II GlV, resistance co4, relay A2, battery and ground.v The contact k2 is now open and the contact Z), is likewise open as the relay B2 will have released its armatures. The -branch is grounded in the first selector at the contact s1, but it is broken in the second selector at the contacts Z), and k3. If a coil is connected in parallel to the contact arms J1 and J2 while this condition exists, a current will flow through the test coil C connected in parallel from the ground, battery in the second selector 11 G`W, relay A2, resistance 10 contact p1, multiple connection, test coil G, multiple connection, contact arm J 2 and back to the ground in the illustrated first selector. The resistance w, now prevents a sufficiently powerful current for the test relay from liowing, while on the other hand this resistance Q02 admits of a holding current sufficient for holding the relay A2.

Let it now be assumed that the third selector has found a free connector. A connector is free when the a-branch of the trunk line is connected to the battery in similar manner as in the selectors and when the -branch is connected to ground. The test coil P31 of the third selector and the relay A2 in the connector attract their armatures, that of the relay A4 disconnecting the Z)- branch of the trunk line from the ground at a., and connecting the relay B2 over the contact c, to the battery. The relays A, and B2 are thus energized. `When the subscriber now rotates his dial for the third time the relay X in the first selector is energized. The contacts a, and are closed and the contact v1 is opened. During the interruptions of the loop in the dial switch the bbranch is kept alive, so that the relay BA1 remains energized during the emission of impulses in the following circuit, viz: ground, battery, relay B4, contacts jz/l, bs and 7) Zi-branch of the trunk line, switch arms J 6, J 4, J2, contacts c5, m4, ground. This circuit over the b-branch keeps the relay B2 in the second selector energized because the relay B2 is connected over the contact p4 and the coil P2 to the b-branch. Consequently, when the interruptions in the dial switch cause the a-branch to be currentless in consequence of the contact a, being opened in the first selector, the second selector remain stationary nevertheless because the releasing circuit was closed only at the same time as the relay B2 released its armatures. The current in the b-branch and the simultaneous absence of current during the impulse in the c-branch causes the relay A 2 iny the connector to release its armature while the relay B2 remains energized. following circuit for the lifting magnet H,1 of the connector is thereby established, viz: ground, battery, lifting magnet H4, contacts al, an, b9, ground, and the connector shaft is lifted. At the termination of the impulses the relay X releases its armatures, the contacts ai, and :v5 are opened, the contacts o, of the relay V remaining open for a time. A current now flows over the z-branch from ground in the first selector l GW, contact s1, resistance we, resistance wg, contacts c2, c4, switch arm J1, c-branch of the trunk line, contacts 775, Q96, relays P, and A2 in the second selector II GlW, battery, ground, in the third selector Hl GliT over switch arm J 3, relay A3, battery, ground and, in addition, in the connector over switch arm J 5, contact p8, resistance w8, contact y2, relay A4, battery and ground. In the second selec- The lays A, A2, A3 and A4 are energized.

The connection into circuit of the resist-y ances w4 and ws has the same obj ect of causing the busy condition as described for the second selector. Owing to the b-branch in the connector being currentless the relay B4 releases its armature. f rlhe relay U is thereby energized over the following circuit, viz: ground, battery, relay U, contact am, 7210, the contact 7c5 closed at the first lifting step of the connector LV, ground. The relay U closes its make contact u, and remains energized independently of the state of the relay B4 until the connector opens the contact 7c5 again when falling back into its normal position. The relay U changes the contact u, over to w3. When the relay V in the first selector releases its armature a moment later, the contact e, is closed and the bbranch is grounded again and current flows again over ground in the irst selector l GV, contact s4, resistance w, over the 7)- branch, contact 202, relay P2, contact p4, relay B2, battery, ground to the relay B3 in the second selector, and also over switch arms J4, J6, contacts p7, a9, g/l, relay B4, battery, ground. The relays B2, B4 attract their armatures. When the subscriber rotatesV his dial again the relay X also attracts its armature. The contact x4 in the first selector closes againand the contact e, is opened again. The current remains in the -branch of the trunk line because it is grounded over the contact m4. The current in the a-branch is interrupted just as frequently as the contact a4 in the first selector is opened in consequence of the interruptions in the dial switch. Each time the circuit is broken the relay A2 in the second selector and the relay A4 in the connector become currentless. The current in the second selector produces no effect, but in the connector the rotary magnet is energized in the following circuit, Viz: ground, battery, rotary magnet D4, contacts a3, 00 b9 and ground. Simultaneously with the rotary magnet D4 the retardation relay V4 is also energized over ground, battery, relay V4, contacts ua, a4, and ground. l

Vhen the relay X is Vcurrentless again after sending the last series of impulses, the contact ai, in the iirst selector opens, but the contact 'v1 remains still open, and the bbranch thus becomes'currentless again. The relay B4 in the connector releases its arma tures. The relay V4 in the connector still remains energized, however, in ccnsequence of its retardation. A testing current for the connector then flows from ground over contacts g1, m3, c3, 72u, relay P3, testing arm of the connector, break contact of the preselector VW of the called subscriber N2,

separating relay T2, to the battery. The test-ing relay P3 of the connector is energized. After some time the contact c, in the irst selector will close again. The relay B4 in the connector is thereby energized again. rlhe rtesting relay P3 ofthe connector remains energized, however, because it has connected itself over its make contact p, into a holding circuit and has short-circuited a part of the winding of the relay P3,

whereby the rcalled line is rendered busy.y

On the test relay P3 being energized the contact p', is made and the cont-act p7 broken. The relay A4 remains energized over the contact y2, resistance w11, contact pg a-branch of the trunk linefand either over contact fc4 or over resistances co5, wf, and contact s, to ground. The -b-branch is currentless at this moment. If the relay V in the first selector then releases its armature and closes the contact c, currentwill flow' again over the ZJ-branch in the following circuit, Viz: ground, contact s4, resistance co7, b-branchv of the trunk line, resistance w10 in the connector, contact a9, contact yl, relay B4, battery, ground. It is of no importance whether the relay B4 is energized over the resistance w40 ornot ,as when both relays A4 and B4 neither simultaneously attract their armatures nor remain deenergized, no further consequences occur. The bridge in the connector thus runs over the a-branch of the trunk line, contact ps, resistance w11, contacts y2, relays A4, B4, contacts fz/l, a, or contact bs, resistance w40, b-branch of the trunk line. As soon as the test relay P3 has attracted its armature it closes a contact p, in the circuit of a calling relay L and contacts p14, and y7911 in the line. While the relay V4 is still energized in consequence of its retardation a rst calling current is produced for the called subscriber in the following circuit, viz: ground, battery, coil 2 of the relay L, contacts e4, '29 g3, 764, and ground, the Contact 706 having closed at the first lifting step of the connector. The relay L breaks the contact Z1 and Z, and makes the contacts 72 and 7 4, and thereby at the moment of testing sends a calling current to the called subscriber. l/Vhen the relay V4 vhas released its armature additional periodic impulses of calling current are sent owing to the excitation of the coil l of the relay L over ground, battery, interrupter U4, coil l, contacts p9, g/S, k6 and ground. This periodic calling current lasts until the called` subscriber lifts his receiver. A circuit is thereby made as follows, Viz: ground, re# lay F, 'contacts Z4, p40, the called line, contacts p11, Z3, coil l of the relay Y, battery and ground. The relaysli and Y in this circuit attract their armatures. The' relay Y first interrupts the calling current by opening the contact y, and making the contact 3/4 and energizing its (Very weak) hold-Y ing coil 2 over ground, battery, coil 2, contacts g4 and las, and ground, this coil 2 being denergized at the release of the connector even when the called subscriber prematurely replaces his receiver. The relay Y also breaks the contacts y2 and y, and makes the contacts y, and jz/. The relays A4 and B,k now release their armatures. Instead thereof an inductively wound relay O, having the middle of its winding grounded, is connected into circuit. The coils of this relay are wound inductively, i. e. non-differentially. The ground at the relay O in the connector is now in parallel with the ground at the contacts s, in the first selector at the talking branches of the trunk lines. The bridge in the second and, under certain circumstances, also in the third selector provides the battery for the further excitation of the relays A2, B2, A3, B3 in the selectors. The resist ances of the coils of the relay O and the resistances w11, w10 in the connector are so great, however, that the relay O cannot attract its armature. y

In case the called subscriber should not be disengaged thetest relay P3 of the connector cannot be energized. The talking wires are then not connected through at the contacts p10, p1, and the calling subscriber receives a buzzing signal over a shaft contact wir, and the contact p12. In the illustrative embodiment the connector does not return into its normal position, but the testing circuit remains open as the relay V, opens the contact v3 after a short time.

Let it be assumed that the called subscriber replaces his receiver before the calling subscriber. The relay F is then denergized. The relay Y remains energized, however, over its holding coil Y2. The following circuit for a relay G is closed, viz: ground, battery, relay G, contacts 1 7, f, and ground. The relay G breaks the contact g, and opens the circuit of the relay P3. The contacts p10 and p11 and 292 open. The called subscriber thereby becomes perfectly free. He can be called by another party, and can himself call although the connector still remains on his line. IVhen the calling subscriber replaces his receiver the relays A and B in the first selector are denergized. On the relay B being denergized the contact Z212 closes and the relay S is thereby energized in the following circuit, viz: ground, contact Z212, the contact 747, closed at the first lifting step of the first selector, relay S, battery and ground. The conversation which has taken place is now metered and the connection is'then done away with.

In the first selector the ground is disconnected at the contact 8 and by closing the contact 8 of the relay S a meter relay Zr in the first selector is connected into circuit. The ground at the relay O is now the sole ground connection in the connectorl and must therefore now supply current lfor the meter bridge in the first selector and for the bridge-connected relays A2, B2 inthe second, and the relays A3, B3 in the third selector. The current in the relay C is thereby strengthened to such an extent that the relay -C attracts its armatures. The meter relay Zr in the first selector operates at the same time, however. This relay Zr closes its contact er, in the selector and thereby short-circuits the resistance 10,. The eurrent in the testing line C thereby increases to such an extent that the meter Z is energized over the following circuit, viz: ground, battery, contact t1, meter Z, c-line, contacts er1, s2, wc2, m2 and ground. When the short circuit of the contact s2 over the relay C in the first selector has acted for a time the relay C releases its armature. The contacts c, and c5 are thereby opened and the switch arms J1, J 2 are separated from the apparatus in the selectors. At the same time the following circuit for the releasing magnet of the first selector is closed7 viz: ground, battery, magnet M, contacts 8 bm, c6, ground. This circuit is opened again only on the arrival of the shaft of the selector into its normal position when the circuit for the relay S has been opened at contact 7c?, and the Contact 84 is subsequently broken. IVhen the releasing magnet M is energized it opens the contacts m, and m2. The holding current for the cut-out magnet T of the preselector or line switch VIV is thereby interrupted whereupon this switch returns into its normal position.

The connector is released owing to the relay C being energized. The following circuit containing releasing magnet M L is thereby closed, viz: ground, battery, magnet M4, contacts yg, 01, ground. When the shaft of the connector arrives into its normal position the contacts 705, k6 and 768 are opened. rlhe relays U and Y are thereby denergized and the releasing magnet M4 likewise becomes currentless. As soon as the relay Y is denergized the relay C is disconnected at the contacts g/5 and g/;,. The battery is again connected over the relays A4 andJBpto the trunk line and now the trunk line is not grounded at all either in the first selector or in the connector. The bridges in the selector are therefore currentless. In the second selector the releasing circuit is closed over ground, battery, rebleasing magnet M2, contacts all, p2, '65, la@ ground, and in the third selector over ground, battery, releasing magnet M3, contacts 612, p13, Z214, lc, and ground. These circuits remain established until the shafts of the selectors open the contacts 7c, and 7c, on its arrival into its normal position. All the switching apparatus have then been returned into their normal positions.

If the required subscriber has not lifted his receiver or it the desired subscribers line was engaged metering is prevented as yfollows. ln this case the relay Y is not energized. The relay@ is thus not connected to the trunk line. Under these circumstances, when the calling subscriber replaces his receiver the relays fi and B in the first selector become currentless, the relay S is energif/cd and ground is cut olip at the contact 31. The relay Zr is not energized, however, because in the connector no reversal o1c the battery over the relays AA, and B to ground over the relay O has taken place. Under these circumstances the battery is still connected to the trunk line in all the selectors. The selectors at once begin to release in consequence of the trunk line being currentless and the relays A, and B, also release their armatures. As mentioned above, the relay B4 may be already denergized, but in any case the relay A, is now also deenergized. The following releasing circuit in the connector is thereby now closed, viz: ground, battery, releasing magnet M4, contacts ys, 515, als, 76S and ground. rl`he contact 768 is broken when the sha-tt of the connector has returned into its normal position.

I claim l. In an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors for interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays `associated with the trunk lines and having coils adapted to be connected at the one end to the one talking wire of the trunk line and the other end to the other talking wire, and means associated with the trunk lines for taking reduced potential to said talking wires when the trunk line is busy.

2. ln an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors for interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays associated with the trunk lines and having coils adapted tor be connected at the one end to the one talking wire of the trunk line and the other end tothe other talking wire, battery-conductors associated with the trunk lines for supplying testing potential to the talking wires, and resistances in said battery-conductors for Arecucing the test potential when the trunk lines are busy.

3. ln an automatic telephone system coni-V the trunk lines of test relays associated withy the trunk lines and having coils adapted to be connected at the one end to the one talking wire of the trunk line and the other end to the other talking wire, battery-conductors associated with the trunk lines for supplying testing potential to the talking wires, resistances in said battery-conductors for reducing the test potential when the trunk lines are busy, and short-circuits associated with said battery-conductors for short-circuiting said resistances when kthe trunk line is free.

4. ln an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors for interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays associated with the trunk lines and having coils adapted to be connected at the one end to the one talking wire and at the other end to the other talking wire and adapted to produce in both talking wires an equal drop of potential for avoiding clicking noises during the testing process, and means associated with the trunk lines for taking reduced potential to said talking wires when the trunk line is busy.

5. ln an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors :tor interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays associated with the trunk lines and adapted to be connected to the talking wires, circuits associated with the trunk lines for producing a locking circuit in the one talking wire for locking and supervising the connection established by the selectors, holding relays for locking and supervising the connection, resistances in said circuits for producing a drop of potential when the line is occupied, said resistances being of such magnitude that the holding relays will retain their armatures and the test relays will not be energized, and means for producing a sending and changeover circuit in the other wire of the trunks.

6. In an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors for interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays associated with the trunk lines and having coils adapted to be connected at the one end to the one talking wire of the trunk line and the other end to the other talking wire, two battery-conductors of equal potential each connected to one of the talking wires, and means associated with the trunk lines for changing the potential in one of said conductors when the trunk line is busy.

7: In an automatic telephone system comprising telephone lines, trunk lines each having two talking wires, and switches and selectors for interconnecting said telephone lines with trunk lines, the combination with the trunk lines of test relays associated with the trunk lines and .having coils adapted to be connected at the one end to the one talkone potential from the one talking wire and lo ing wire of the trunk line and the other end to Connect the battery-conductor of clieient to the other talking wire, two batteiy-Conpotential to the Same talking wire.

cluetoi's of equal potential each connected to In testimony whereof, I aix my Signature one of the talking wires, a third batteryin the presence of two witnesses.

conductor of different potential, and a test MAX LANGER. relay in one of the two battery-conductors, Witnesses:

the latter relay being adapted when eneil/VOLDEMAR HAUPT,

gizecl to disconnect the battery-conductor of HENRY HASPER. 

